Spraying devices



INVENTOR @ZJXUM ATTORNEY United States Patent Office 3,010,428 PatentedNov. 28, 1961 3,010,428 SPRAYING DEVICES John I; Sedlacsik, Garfield,NJ., assignor to Interplanetarry-Research & Development ;Corp.,Garfield, NJ., a corporation of New Jersey Filed Sept. 10, 1957, Ser.No. 683,040 Claims. (Cl. 118-626) This invention relates to the sprayingof coating liquids and, more particularly, to a spraying device in whichthe liquid is dispersed by a rotating member or rotor and thentransmitted by an electrostatic field to the object to be sprayed.

Heretofore, the rotating member or rotor was made of metal and chargedwith a high electric potential so that the liquid would be ionized as itleft the rotating member. Much of the electrical energy is lost by thismethod because the rotary member acts like the plate of a capacitor,causing large leakage losses between the device and the work piece.

An object of this invention is to provide an electrostatic sprayingdevice with only a minimum of electrical energy losses.

Another object of this invention is to obtain, with this type of device,a uniform coating at a high rate of deposition.

The foregoing objects and others ancillary thereto I prefer toaccomplish as follows:

According to one embodiment of this invention, the

rotating member or rotor is made of a suitable ametal-' lous materialhaving a'high electric resistivity. A narrow metallic ring or electrodeis mounted coaxially with the rotating member and is located adjacent tothe circumference of the rotating member. This ring is attached to thespraying device and to the negative terminal of a high voltageelectrical supply.

The article to be coated is attached or grounded to the positiveterminal and insulated relative to the ring, thus establishing "anelectrostatic field between the ring and thetarticle to be coated- Sincethe area of the ring is small, most of the energy is utilized in theformation of acorona discharge ionizing the air surrounding the ring. Asthe member rotates, the liquid, which is supplied to the member adjacentthe axis of rotation thereof, moves toward the circumferential edge ofthe member in the form of a film. As the liquid passes between the ringand the rotating member, the particles thereof become negativelycharged. This causes a molecular repulsion which disperses the particlesof liquid in a line mist or fog. The article to be coated, beingpositively charged, attracts and is enveloped by the fog, thus coatingall exposed portions of the article.

This preferred embodiment of the invention is set forth in theaccompanying drawings, in which:

FIG. 1 is a sectional view of the invention;

FIG. 2 is a sectional view of a modified form of the invention; and

. FIG. 3 is a detail sectional view of the ring-supporting collar.

An electrostatic sprayer to overcome the defects here-- inbeforementioned must have an electrically charged member of a small surfacearea and of such a configuration as to produce the desired coronadischarge at the periphery of the rotating member. Accordingly, theinvention, as shown in FIG. 1, is constituted by an ametallous member orrotor 4 having a substantially frustumshaped outer section 5. The rotor4 is rotatably mounted on a shaft 6 and with a stationary metallic ring7 located at the outer edge of the rotor 4 in spaced relation therewith.

A stationary housing or tube 8 constructed of an ametallous materialhaving a high electric resistivity has mounted therein the rotatableshaft 6 journaled in bearings (not shown) in the tube 8, so that theshaft 6 is free to rotate Within the tube. The lower end portion of theshaft 6 projects from the tube 8, and said projecting end of the shaft 6is provided with a flange 9 and a threaded portion 10 therebelow. Therotor or member 4 is afiixed to the shaft-6 by means of a washer 11 anda nut 12 cooperating'with the flange 9. Thus, when the shaft 6 isrotated by an electric motor, or other suitable means, the rotor 4 willbe rotated by the shaft. Suitable insulation may also be providedbetween the motor shaft and the shaft 6. Furthermore, the housing 8 maybe constructed of metal and insulated from the motor or other componentsto preclude arcing, etc.

The metal ring 7 is mounted on the stationary tube 8 by means of acollar 13 having a sleeve 14 extending therethrough. Several round wirebracket rods 15 are welded at one end to the ring 7, and this assemblyis attached to the collar '13 by the rods 15 being inserted at theiropposite ends into holes 16 and secured and held therein by set screws17. The metal ring 7 is positioned in the plane of, and adjacent to, theouter edge of the rotor or member 4.

Referring now to FIG. 2, a modification of the invention, the metal ringv19, which is to carry the electric charge, is in the shape of a frustumof a cone, while the rotating member or rotor 20 is provided with anouter flat discal section 21. The rotor 20 is attached to the shaft 6 bythe washer 11 and the nut 12, so that the rotor will rotate with theshaft. The metal ring 19 is attached to the stationary tube 8 by meansof the collar 13 and by wire bracket rods 22 having coincident slottedor bifurcated ends receiving the ring 19 and being clampriveted to thering. This assembly is attached to the collar 13 by inserting the otherends of the rods 22 into the holes 16 and securing the same therein bythe set screws 17.

A wire 23 from a high voltage supply V, as diagrammatically shown, isattached directly to the metal ring 7, as shown in FIG. 1, or to thesupporting rods 22, as shown in FIG. 2. The metal rings 7 and 19 areeach provided at its outer circumference with a sharp edge 24 and arounded edge at its inner circumference. This configuration results inthe most efficient electric discharge pattern and concentrates thedischarge at the circumferential edge of the rotor to provide the coronadischarge.

Both of the rotors 4 and 20 are each provided with a cup-shaped inner orcentral portion 25 defining a. chamber 26 having a side wall with aslight outward slope and having a larger diameter at its mouth than atthe bottom of the chamber. This configuration is desirable to allow thecoating liquid to flow up the side wall of the chamber in a uniform filmby centrifugal force as the rotor turns at high speed- In operation, therotor is rotated by the shaft 6, and a high electrical potential isapplied to the metal ring 7 or 19 to the extent of producing a coronadischarge at the edge 24 of the ring. Coating liquid is supplied to thechamber 26 of the rotor through a conduit 27, made of an electricallyinsulating substance. In some instances, coating liquid may be mixed inthe chamber 26. The conduit 27 extends through the sleeve 14 and is thusattached to the stationary tube '8 by the collar 13. Since the chamberis rotating at a high speed, centrifugal force will cause the coatingliquid to flow up its wall in a film of uniform thickness. As the liquidreaches the mouth of the chamber of the rotating member, it movesradially more violently and rapidly, since there is little or norestraint on it. Also, as the liquid moves outwardly, it will spreadover an increasingly larger area and the film will thin outproportionately. As the film passes beyond the metal ring 7 or 19, whichis maintained at a high negative potential, the particles are thoroughlyelectrified by the corona discharge. All the particles, being of thesame polarity, explode and are repelled by each other and by the ringitself, forming a fine mist or fog which is attracted to the article Ato be coated, since it is grounded andof the opposite polarity.

The usual practice is to mount the spraying device adjacent a movingconveyor on which are positioned the articles to be coated. If thearticles are larger than the effective coverage area of the sprayingdevice, the latter is secured to a suitable reciprocating apparatus,such as a hydraulic piston with suitable controls for optimum stroke andrate of motion.

As can be seen readily by the foregoing disclosure, this invention hasmany advantages over other sprayers of this type. The location andconfiguration of the metal rings concentrates the electrical energy atthe point of maximum effectiveness for liquid dispersion. Also there islittle electrical energy lost because the area of the highly chargedsurface is small. These factors will result in more economical operationof the sprayer and in more even coating.

I claim:

1. An electrostatic sprayer apparatus for spraying an article to "becoated, said apparatus including a rotor made of an electricallynon-conductive material having an annular coating material dischargeedge and adapted to centrifugally project particles of coating materialsubstantially radially outwardly therefrom, an annular chargingelectrode having an outwardly projecting continuous sharp edge spatiallydisposed, adjacent, and subtsantially parallel to said coating materialdischarge edge to charge and repel the particles of coating material asthey are centrifugally projected in the form of an atomized sprayfrom'the rotor material discharge edge, means to apply coating materialto said rotor, and means to apply one polarity of a high potential tothe article to be coated and an opposite polarity to said annularcharging electrode, whereby the centrifugally projected coating materialin the form of an atomized spray at no time is subjected todirectelectrical contact with the annular charging electrode and whereinthe centrifugally atomized parti'cles of coating material are directlycharged electrostatically' by the annular charging electrode after beingcentrifugally atomized.

2. Apparatus for use in a system for spraying articles to be coated'withparticles of coating material and wherein said articles are electricallycharged at one polarity and adapted to be coated by particles of coatingmaterial of a different polarity, comprising a centrifugal atomizer andincluding an element of non-conducting material and having a peripheralcoating material discharge edge for centrifugal atomization therefrom ofcoating material to be mechanically projected toward said articles, anda charging electrode having a continuous sharp edge spatially disposedfrom and adjacent said coating material discharge edge, said chargingelectrode being adapted to be electrically charged at a predeterminedpolarity to establish an electrostatic field adjacent said centrifugalatomizer material discharge edge to charge said centn'fugally atomizedparticles for electrostatic deposition with at least a portion ofnon-conducting material and.

adapted to receive and centrifugally discharge therefrom Said coatingmaterial, said centrifugal atomization element means having an annularperipheral edge for the discharge therefrom of said coating material incomminuted form, charging electrode means having a metallic continuoussharp charging edge means spatially disposed from but adjacent saidperipheral edge of the centrifugal atomization discharge element,whereby when said charging electrode means is charged at the electricalpolarity oppoiste to that of said article, said coating materialparticles will be charged at the same polariy as the charging electrodemeans upon emanation of said coating material in atomized form from saidcentrifugal atomizing element means having said portion of nonconductingmaterial to coat said article-with said charged particles of coatingmaterial without said coating material coming into direct electricalcontact with the charging electrode means.

4. An atomizer head for use in centrifugal atomization andelectrostatically changing material for spray coating an article withcharged particles of one polarity of coating material emanating fromsaid atomizer head and attracted electrostatically to an article chargedof the polarity opposite to that of the charged particles, said atomizerhead including a rotatable element having at least a mate rial dischargeedge of ametallous material for centrif ugally discharging radiallytherefrom particles of coating material in atomized form, andelectrically conductive means having a continuous peripheralelectrostatic charging edge spatially disposed from said materialdischarge ';edge of the ametallous rotating element and adjacent theretoto electrostatically directly charge, when energized, said particles ofcoating material discharged therefrom, and while in transit to thearticle to be coated beyond the confines of the coating materialdischarge edge.

5. An electrostatic spraying device for spraying articles to be coatedwith particles of coating material comprising rotor and stator elementsarranged coaxially and each having adjacent edge portions disposedrespectively equidistant and in a predetermined spatial relationadjacent to one another for establishing a uniformcorona dis-- chargearea therebetween, said rotor element being substantially disc-shapedand adapted to provide an annular spray centrifugally projected fromsaid edge portion, said.

stator element having its said edge portion terminating in asubstantially sharp peripheral edge spatially disposed and adjacent saidrotor edgeportion, means for coupling a source of high potential withthe stator element for establishing a corona discharge in said coronadischarge area for electrostatically charging the particles of coatingmaterial as they are centrifugally projected in the form of an atomizedspray from said rotor, and means for supplying coating material to therotor element, said rotor element being made of substantiallyelectrically non-conducting material to, prevent the coating materialapplied thereto from direct contact with said source of high potential,whereby atomization in the form of a spray of the coating material isproduced centrifugally by said rotor element of substantiallyelectrically non-conducting material and the particles of said spray aredeposited predominately by References Cited in the file of this patentUNITED STATES PATENTS Ransbur-g Nov. 3, 1953 Sedlacsik June 14, 1955Juvinall Aug. 21, 1956 6 Iuvinall Sept. 25, 19 56 Ju-vinall Feb. 5, 1957Miller Feb. 12, 1957 Juvinall et a1. Mar. 10, 1959 Norris Aug. 25, 1959Norris Aug. 25, 1959 FOREIGN PATENTS Great Britain June 23, 1954

